U.S. patent application number 14/916465 was filed with the patent office on 2016-07-28 for method for operating cement plant.
This patent application is currently assigned to MITSUBISHI MATERIALS CORPORATION. The applicant listed for this patent is MITSUBISHI MATERIALS CORPORATION. Invention is credited to Takuya KOMATSU, Yoshinori TAKAYAMA.
Application Number | 20160214893 14/916465 |
Document ID | / |
Family ID | 52742410 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160214893 |
Kind Code |
A1 |
KOMATSU; Takuya ; et
al. |
July 28, 2016 |
METHOD FOR OPERATING CEMENT PLANT
Abstract
There is provided a method for operating a cement plant capable
of simultaneously optimizing both combustion in a calciner and a
heat consumption rate. The method for operating a cement plant
includes: feeding first fuel to a calciner; feeding second fuel for
maintaining the inside at a burning temperature to a cement kiln
along with combustion primary air, and introducing air for cooling
cement clinker to a cooler; and feeding a part of the air as
secondary air to the cement kiln, feeding as tertiary air to the
calciner, and discharging the rest of the air from the cooler,
wherein relation between a first oxygen concentration at an exhaust
gas outlet of the calciner and a heat consumption rate determined
by the first fuel and the second fuel, and relation between a
second oxygen concentration at an exhaust gas outlet of the
preheater and the heat consumption rate are beforehand obtained,
and amounts of the secondary air and the tertiary air are adjusted
such that both the first oxygen concentration and the second oxygen
concentration fall within a range including values of the oxygen
concentrations at which the heat consumption rate becomes at its
minimum.
Inventors: |
KOMATSU; Takuya; (Naka-shi,
JP) ; TAKAYAMA; Yoshinori; (Naka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI MATERIALS CORPORATION |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI MATERIALS
CORPORATION
Chiyoda-ku, Tokyo
JP
|
Family ID: |
52742410 |
Appl. No.: |
14/916465 |
Filed: |
June 30, 2014 |
PCT Filed: |
June 30, 2014 |
PCT NO: |
PCT/JP2014/003457 |
371 Date: |
March 3, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F23N 2223/40 20200101;
F27D 2017/009 20130101; C04B 7/434 20130101; F27B 7/10 20130101;
F23N 5/006 20130101; F27D 99/0033 20130101; C04B 7/006 20130101;
C04B 7/4407 20130101; F27B 7/20 20130101; C04B 7/4407 20130101;
C04B 7/47 20130101 |
International
Class: |
C04B 7/43 20060101
C04B007/43; C04B 7/00 20060101 C04B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2013 |
JP |
2013-204005 |
Claims
1. A method for operating a cement plant which includes a preheater
that preheats a raw material, a calciner that calcines at least
part of the raw material picked out of the preheater, a cement kiln
that burns the raw material passed through the preheater and the
calciner into cement clinker, and a cooler that cools the cement
clinker discharged from the cement kiln, the method comprising:
feeding first fuel in an amount required for calcining the
introduced raw material to the calciner; feeding to the cement
kiln, along with combustion primary air, second fuel in an amount
required for maintaining an inside of the cement kiln at a burning
temperature, and introducing air in a certain amount for cooling
the cement clinker to the cooler; and feeding a part of the air as
secondary air for assisting combustion of the second fuel to the
cement kiln, feeding another part of the air as tertiary air for
combustion of the first fuel to the calciner, and discharging the
rest of the air from the cooler, wherein relation between a first
oxygen concentration at an exhaust gas outlet of the calciner and a
heat consumption rate determined by the first fuel and the second
fuel, and relation between a second oxygen concentration at an
exhaust gas outlet of the preheater and the heat consumption rate
are beforehand obtained, and flow rates of the tertiary air and
exhaust from the cooler are adjusted such that both the first
oxygen concentration and the second oxygen concentration fall
within a range including values of the oxygen concentrations at
which the heat consumption rate becomes at its minimum.
2. The method for operating the cement plant according to claim 1,
wherein the first fuel is fed to the calciner at a certain feed
amount, and the second fuel is adjusted at a feed amount required
for maintaining it at the burning temperature and fed to the cement
kiln.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for operating a
cement plant including a calciner.
BACKGROUND ART
[0002] Conventionally, there is known a cement plant in which an
auxiliary combustion furnace (hereinafter referred to as calciner
in the description) is provided upstream of a cement kiln that
burns a raw material, so that a part of the raw material preheated
in a preheater is heated to promote decarbonation (for calcining),
and thereby, load on the cement kiln is reduced.
[0003] Further, an operation method is proposed, for example, in
Patent Literature 1 below for efficiently burning fuel (pulverized
coal or the like) inputted to the calciner in a cement plant in
which the calciner of this type is provided.
CITATION LIST
Patent Literature
[0004] Patent Literature 1: Japanese Patent Publication No.
2-22016
SUMMARY OF INVENTION
Technical Problem
[0005] However, in the conventional method for operating the
aforementioned cement plant, when amounts of pulverized coal and
combustion air inputted to the calciner are in excess for
optimizing combustion in the calciner, although a reaction ratio of
the raw material in the calciner increases, sensible heat of the
exhaust gas discharged from the calciner increases instead, which
causes increase of a heat consumption rate (heat amount required
for producing 1 kg of clinker) which is a heat consumption amount
in the whole burning process, and thus, problematically causes high
production costs.
[0006] The present invention is devised in view of the
aforementioned circumstances, and an object thereof is to provide a
method for operating a cement plant capable of simultaneously
optimizing both combustion in a calciner and a heat consumption
rate
Solution to Problem
[0007] Typically, in a cement plant, fuel required for maintaining
the inside at the burning temperature of a raw material is fed
through a main burner of a cement kiln along with combustion air
(primary air), and cooling air is fed to a cooler for cooling burnt
clinker at a certain flow rate. Further, a part of the air which
becomes at high temperature by heat exchange with the clinker in
the cooler is fed inside the cement kiln as secondary air for
assisting the combustion air, another part of the air is fed to the
calciner as combustion air (tertiary air), and the rest of the air
is directly discharged from the cooler.
[0008] Accordingly, for example, when the flow rate of the
combustion air fed to the calciner is increased, the exhaust flow
rate from the cooler decreases. Further, increase of the flow rate
of the combustion air in the calciner causes increase of the flow
rate of the preheater exhaust gas discharged from the preheater,
which results in a high value of the heat consumption rate.
Conversely, when the flow rate of the combustion air fed to the
calciner is reduced, the flow rate of the direct exhaust from the
cooler increases, and therefore, latent heat of the exhaust gas
that has become at high temperature by heat exchange with the
clinker is not used to be discarded, which similarly causes a poor
heat consumption rate.
[0009] Regarding the above, the inventors have obtained a knowledge
that since when the cooling air is fed to the cooler at a certain
flow rate, increases or decreases of the exhaust gas from the
preheater and the exhaust gas from the cooler are in trade-off
relation in the whole burning process, the heat consumption rate
can be made at its minimum if the flow rate of the tertiary air is
adjusted such that the sum of the sensible heats of these exhaust
gases becomes at its minimum.
[0010] However, in actual operation of the cement plant, it is
difficult to directly detect the flow rates of the exhaust gas from
the preheater and the exhaust gas from the cooler.
[0011] Meanwhile, an oxygen (O.sub.2) concentration meter is
typically installed at the exhaust gas outlet of the calciner for
confirming the combustion state in the calciner.
[0012] Regarding the above, the inventors have obtained a knowledge
that relation between the O.sub.2 concentration in the exhaust gas
from the preheater and the heat consumption rate and relation
between the O.sub.2 concentration in the exhaust gas from the
calciner and the heat consumption rate can be obtained by
calculating material balances and the heat consumption rate in the
whole burning process in process simulation where each of the
facilities such as the preheater, the calciner, the cement kiln and
the cooler in the cement plant is divided into units called unit
operations and a macroscopic reaction and heat exchange in each
facility are described.
[0013] The present invention is achieved based on such knowledge as
above, and the invention according to claim 1 is a method for
operating a cement plant which includes a preheater that preheats a
raw material, a calciner that calcines at least part of the raw
material picked out of the preheater, a cement kiln that burns the
raw material passed through the preheater and the calciner into
cement clinker, and a cooler that cools the cement clinker
discharged from the cement kiln, the method comprising: feeding
first fuel in an amount required for calcining the introduced raw
material to the calciner; feeding second fuel in an amount required
for maintaining an inside at a burning temperature to the cement
kiln along with combustion primary air, and introducing air in a
certain amount for cooling the cement clinker to the cooler; and
feeding a part of the air as secondary air for assisting combustion
of the second fuel to the cement kiln, feeding another part of the
air as tertiary air for combustion of the first fuel to the
calciner, and discharging the rest of the air from the cooler,
wherein relation between a first oxygen concentration at an exhaust
gas outlet of the calciner and a heat consumption rate determined
by the first fuel and the second fuel, and relation between a
second oxygen concentration at an exhaust gas outlet of the
preheater and the heat consumption rate are beforehand obtained,
and flow rates of the tertiary air and exhaust from the cooler are
adjusted such that both the first oxygen concentration and the
second oxygen concentration fall within a range including values of
the oxygen concentrations at which the heat consumption rate
becomes at its minimum.
[0014] Moreover, the invention according to claim 2, which is
according to claim 1, is characterized in that the first fuel is
fed to the calciner at a certain feed amount, and the second fuel
is adjusted at a feed amount required for maintaining it at the
burning temperature and fed to the cement kiln.
[0015] Notably, in the present invention, the heat consumption rate
is the sum total of the heat amounts of pulverized coal, oil coke
and the like which are inputted to the cement kiln and the calciner
and required for producing 1 kg of clinker. More specifically, it
is obtained based on the sum of the product of the calorific value
per unit weight of the fuel such as pulverized coal inputted to the
cement kiln and the input amount thereof and the product of the
calorific value per unit weight of the fuel such as pulverized coal
inputted to the calciner and the input amount thereof.
Advantageous Effects of Invention
[0016] According to the invention recited in claim 1 or 2, relation
between the first oxygen concentration at the exhaust gas outlet of
the calciner and the heat consumption rate determined by the first
fuel and the second fuel, and relation between the second oxygen
concentration at the exhaust gas outlet of the preheater and the
aforementioned heat consumption rate are beforehand obtained and,
in operation, the first oxygen concentration and the second oxygen
concentration are measured, and the flow rate of the tertiary air
fed to the calciner from the cooler and the exhaust flow rate from
the cooler are adjusted such that both of these concentrations fall
within a range including the values of the oxygen concentrations at
which the heat consumption rate becomes at its minimum. By the
adjustment described above, both the combustion in the calciner and
the heat consumption rate can be simultaneously optimized.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a schematic configuration diagram of a cement
plant to which an embodiment of the present invention is
applied.
[0018] FIG. 2 is a schematic diagram of an unreacted core model
used in simulation of the aforementioned embodiment.
[0019] FIG. 3 is a graph illustrating relation between an O.sub.2
concentration in exhaust gas at a calciner outlet and sensible heat
of cooler exhaust.
[0020] FIG. 4 is a graph illustrating relation between the O.sub.2
concentration in the exhaust gas at the calciner outlet and
sensible heat of preheater exhaust gas.
[0021] FIG. 5 is a graph illustrating relation between the O.sub.2
concentration in the exhaust gas at the calciner outlet and a heat
consumption rate.
[0022] FIG. 6 is a graph illustrating relation between the O.sub.2
concentration in the exhaust gas at the preheater outlet and the
heat consumption rate.
DESCRIPTION OF EMBODIMENTS
[0023] First, a configuration of a cement plant to which an
embodiment of the present invention is applied is described based
on FIG. 1. The cement plant is schematically configured of a
preheater 1 preheating a raw material, a calciner 2 calcining at
least part of the raw material picked out of the preheater 1, a
cement kiln 3 burning the raw material passed through the preheater
1 and the calciner 2 into cement clinker, and a cooler 4 cooling
the cement clinker discharged from the cement kiln 3.
[0024] Herein, the preheater 1 has a plurality of (in the figure,
four stages of) cyclones 1a to 1d joined in the vertical direction,
and is a facility preheating the raw material whose particle size
and components are adjusted in a raw material process and which is
fed to the uppermost cyclone 1a from a feed line 5 with gas at high
temperature discharged from the cement kiln 3, in the process of
sequentially feeding to the downward cyclones 1b to 1d.
Incidentally, the raw material which has been inputted to the
uppermost cyclone 1a at a temperature of approximately 80.degree.
C. reaches the lowermost cyclone 1d to have a temperature of
800.degree. C. or more, which leads to decarbonation of limestone
as well as preheating.
[0025] Meanwhile, in an exhaust line 6 for preheater exhaust gas
discharged from the uppermost cyclone 1a, a not-shown fan is
provided, and the preheater exhaust gas is configured to be
discharged outside the system by suction of the fan. The preheater
exhaust gas is discharged outside the system after heat exchange of
combustion exhaust gas discharged from the cement kiln 3 and the
calciner 2 and CO.sub.2 generated by the decarbonation of the raw
material with the raw material between the lowermost cyclone 1d and
the uppermost cyclone 1a. In the exhaust line 6, an O.sub.2
concentration meter 6a measuring an O.sub.2 concentration (second
O.sub.2 concentration) in the preheater exhaust gas is provided.
This preheater exhaust gas sensible heat affects, as a heat loss,
the heat consumption rate which is a heat consumption amount in the
whole system.
[0026] Moreover, the calciner 2 partially takes the raw material
heated until the preheater 1c from a line 7 to perform the
decarbonation in order to reduce heat load on the cement kiln 3.
The calciner 2 gives heat to the raw material, in which calciner
pulverized coal (first fuel) 8 inputted thereto burns with high
temperature tertiary air 10 recovered from the cooler 4 via an
exhaust line 9. Then, the raw material, unburnt pulverized coal,
and exhaust gas which are discharged from the calciner 2 are
configured to be introduced into the lowermost cyclone 1d of the
preheater 1 via a line 17. In the relevant line 17, an O.sub.2
concentration meter 2a measuring an O.sub.2 concentration (first
O.sub.2 concentration) in the exhaust gas from the calciner 2 is
provided. Moreover, in the exhaust line 9, a flow rate adjusting
valve 11 is provided for controlling a flow rate of the tertiary
air 10.
[0027] The aforementioned cement kiln 3 is a cylindrical member
which is driven and rotated around its axis line, the inside of
which kiln is configured to be held at 1450.degree. C. required for
burning the raw material with the combustion gas and radiation from
the flame by the raw material heated in the preheater 1 and the
calciner 2 being fed to a kiln inlet part 3a and by pulverized coal
(second fuel) 13 being fed through a main burner 12 provided in a
kiln outlet part 3b along with primary air for fuel. Then, the raw
material fed into the cement kiln 3 from the kiln inlet part 3a is
heated and completes the decarbonation by heat exchange in the
cement kiln 3 in its sending process to the kiln outlet part 3b
side with the rotation of the cement kiln 3, and is further burnt
to form the cement clinker.
[0028] Further, in the cement kiln 3, an input amount of the
aforementioned pulverized coal is adjusted such that the
decarbonation of the raw material and the clinker burning reaction
can be performed in accordance with the temperature of the raw
material and the decarbonation rate at the inlet, and a flow rate
of the combustion primary air and a flow rate of the combustion
assisting secondary air 15 fed from the cooler 4 are controlled
such that the relevant pulverized coal is completely burnt and the
O.sub.2 concentration in the exhaust gas at the kiln inlet part 3a
takes a predetermined value.
[0029] Next, the cooler 4 is provided for cooling the clinker
discharged from the cement kiln 3, and on its bottom part, cooling
air 14 for rapidly cooling the clinker is configured to be fed. A
certain amount of cooling air 14 is configured to be fed
corresponding to the amount of clinker to be produced. Then, the
clinker cooled in the cooler 4 is discharged to have approximately
150.degree. C. at the cooler outlet.
[0030] Meanwhile, the air 14 used for cooling becomes to have high
temperature by heat exchange with the clinker. A part thereof is
fed to the cement kiln 3 as the combustion assisting secondary air
15 in the cement kiln 3, another part of the air is fed to the
calciner 2 as the tertiary air 10 as mentioned above, and the rest
of the air 16 is discharged outside by a fan provided in a
not-shown exhaust line. Similarly to that of the preheater exhaust
gas, the sensible heat of this exhaust from the cooler 4 also
affects, as a heat loss, the heat consumption rate.
[0031] Further, in the cement plant, relation between the first
O.sub.2 concentration measured by the O.sub.2 concentration meter
2a at the exhaust gas outlet of the calciner 2 and the heat
consumption rate determined by the feed amount of the pulverized
coal 8, 13, and relation between the second O.sub.2 concentration
measured by the O.sub.2 concentration meter 6a at the exhaust gas
outlet of the preheater 1 and the aforementioned heat consumption
rate are beforehand obtained by process simulation analysis
mentioned later.
[0032] Then, the number of revolutions of the aforementioned fan
provided in the exhaust line from the cooler 4 and the degree of
opening of the flow rate adjusting valve 11 provided in the exhaust
line 9 are controlled such that both the first and second O.sub.2
concentrations fall within a range including the values of the
O.sub.2 concentrations at which the heat consumption rate becomes
at its minimum. By this configuration, the amounts of the tertiary
air 10 fed from the cooler 4 to the calciner 2 and exhaust 16
directly discharged from the cooler 4 are adjusted.
[0033] Herein, the aforementioned process simulation performed by
the inventors and others is specifically described. In the process
simulation, each facility is divided into units each of which is
called a unit operation. For example, the cyclone is done into a
separator, a heat exchanger, a reactor and the like. Then, these
are arranged as in a circuit diagram, flows (streams) of solids
(powders) and gases are connected therebetween, and the solution is
obtained by repeating calculations until their final convergence.
Notably, the present process simulation was performed using Aspen
Plus v7.2 of Aspen Tech Corporation, which was general purpose
process simulation software.
[0034] Moreover, for the present process simulation, reaction rate
models were introduced to the calciner 2 and the lowermost cyclone
1d in which the decarbonation of the cement material and the
combustion of the pulverized coal 8 occurred. Moreover, an
unreacted core model was adopted as the reaction model for the raw
material. As illustrated in FIG. 2, the unreacted core model is a
model in which an unreacted part (unreacted core) is present inside
the particle and a reaction product layer is formed on the outside
thereof. Since the reaction rate varies depending on the diameter
of the unreacted core, the calculation in which the variation in
reaction rate depending on the reaction ratio is taken into
consideration can be performed.
[0035] The raw material was configured to have a composition at
which clinker for portland cement could be generally manufactured.
Moreover, CaCO.sub.3 contained in the raw material was configured
to change into CaO due to the decarbonation. Assuming that in the
decarbonation reaction, the reaction occurred on the surface of the
unreacted CaCO.sub.3 and the reaction boundary was proportional to
the surface area, a grain model was adopted.
[0036] In the calculation, taking the influence of diffusion of
CO.sub.2 in the gas boundary film into consideration, an
equilibrium partial pressure P.sub.CO2.sub._.sub.eq of CO.sub.2 at
a predetermined temperature was obtained, and correction was
performed using its ratio relative to a CO.sub.2 partial pressure
in the calculation. As indicated in the following expression, a
reaction amount was calculated based on the product of a reaction
rate coefficient and a retention time. Notably, for temperature
dependency of the equilibrium partial pressure, actual measurements
using a thermogravimetry or the like and/or values, for example, in
literature ("Thermodynamic evaluation and optimization of the
(Ca+C+O+S) system" D. Lindberg and P. Chartrand, J. Chem. Thermo.,
41, 2009) or the like can be used.
k = A exp ( - E RT ) ( 1 - X ) 2 / 3 ( 1 - P CO 2 P CO 2 _ eq ) [
Expression 1 ] ##EQU00001##
[0037] In Expression 1,
[0038] k: Reaction rate [1/s]
[0039] A: 2.2.times.10.sup.8 [1/s]
[0040] E: 2.0.times.10.sup.5 [J/mol]
[0041] R: Gas constant 8.314
[0042] T: Temperature [K]
[0043] X: Decarbonation ratio (on a mass-basis)
[0044] P.sub.CO2: CO.sub.2 partial pressure in the calculation
[0045] P.sub.CO2.sub._.sub.eq: Equilibrium partial pressure of
CO.sub.2 at a predetermined temperature.
[0046] Moreover, the preheater 1 has the cyclones 1a to 1d joined
in the vertical direction, and preheats the raw material with the
combustion gas discharged from the cement kiln 2 at high
temperature. Thus, the raw material which has been inputted to the
uppermost cyclone 1a at a temperature of approximately 80.degree.
C. reaches the lowermost cyclone 1d to have a temperature of
800.degree. C. or more, which leads to the decarbonation of
CaCO.sub.3 as well as preheating.
[0047] Furthermore, in the calciner 2, it was configured that a
certain amount of raw material and a certain amount of pulverized
coal corresponding to this were fed thereto, and the flow rate of
the combustion tertiary air 10 was adjusted. Further, it was
configured that the decarbonation in the calciner 2 occurred as
mentioned above, and the pulverized coal was burnt with reference
to literature ("A random pore model for fluid-solid reactions: I.
Isothermal, kinetic control", S. K. Bhatia, D. D. Perlmutter, AIChE
Journal vol 26, 3 1980) and ("Modeling of coal gasification
reaction: Reaction rate and morphological model of coal char
gasification", Shiroh Kajitani, Report of Central Research
Institute of Electric Power Industry, 2003).
[0048] Moreover, in the cement kiln 3, it was configured that the
input amount of the pulverized coal was adjusted such that the raw
material became the clinker at 1450.degree. C. (burning zone
temperature), the flow rate of the secondary air 15 for assisting
the combustion was determined such that the oxygen concentration in
the exhaust gas at the kiln inlet part 3a was 2% when the
pulverized coal was burnt and discharged from the cement kiln 3 as
the exhaust gas. Incidentally, the value of 1450.degree. C. is a
value at which the clinker burning reaction is typically said to
occur, and the value of 2% of oxygen in the exhaust gas is a
typical target value in operating a cement plant of the type in
which the cement kiln 3 and the calciner 2 are separated.
[0049] Further, inside the cement kiln 3, a heat amount which the
raw material receives from the combustion gas in heating to
1450.degree. C. with the radiation from the flame of the main
burner 12 and the heat exchange with the combustion gas is
indicated by the following expression.
Q=.alpha..times.Q.sub.combustion.sub._.sub.air [Expression 2]
[0050] .alpha.: Heat amount ratio which the raw material receives
from the combustion gas
[0051] Q.sub.combustion.sub._.sub.air: Sensible heat of the
combustion gas [kcal/hr]
[0052] It was configured .alpha.=0.4 in the present embodiment.
[0053] Moreover, the heat exchange between the clinker and the
cooling air 14 in the cooler 4 was calculated as the clinker being
a fixed layer and the flow being in a crossflow manner. The
coefficient of heat transfer was derived from the ranz-marshall
expression. The heat transfer amount Q was calculated by obtaining
the heat transfer amount q between particles and fluid per unit
volume of the stationary layer with reference to literature
("Process kiln", Association of Powder Process Industry and
Engineering, JAPAN, Nikkan Kogyo Shimbun Ltd., 1985), and by
calculating its product with the volume V of the particles and the
correction coefficient F for the crossflow heat exchange obtained
with reference to literature ("Mean temperature difference and
temperature efficiency for shell and tube heat exchangers connected
in series with two tube passes per shell pass", Dodd, R., IChemE,
vol. 58, 1980). The particle diameter of the clinker was configured
to be 20 mm, and the layer thickness of the clinker deposited
inside the cooler was configured to match the thickness in an
actual machine.
Q=qFV=ha.DELTA.TFV [Expression 3]
[0054] where,
[0055] Q: Heat transfer amount [J/s]
[0056] q: Heat transfer amount per unit volume [J/m.sup.3s]
[0057] F: Correction coefficient
[0058] V: Volume of the particles [e]
[0059] h: Coefficient of heat transfer [J/m.sup.2sK]
[0060] a: Specific surface area of the particles [1/m]
[0061] Moreover, in actual operation, combustion management of the
pulverized coal 8 is performed based on the O.sub.2 concentration
in the exhaust gas from the calciner 2. Hence, the calculation in
the case where the flow rate of the tertiary air 10 was adjusted
such that the O.sub.2 concentration in the exhaust gas of the
calciner 2 became 1.5% to 5% according to the actual operation was
performed.
[0062] As a result, as illustrated in FIG. 3, since the flow rate
of the tertiary air 10 recovered as the combustion air of the
calciner 2 increases in the cooler 4, the exhaust flow rate from
the cooler 4 decreases, and the temperature decreases, which causes
decrease of the sensible heat of the exhaust gas.
[0063] Moreover, as illustrated in FIG. 4, when the flow rate of
the tertiary air 10 to the calciner 2 is increased, take-away
sensible heat from the preheater increases due to increase of the
preheater exhaust gas temperature caused by increase of the exhaust
gas temperature at the outlet of the lowermost cyclone 1d, and in
addition to this, due to increase of the combustion air flow
rate.
[0064] FIG. 5 illustrates variation of the heat consumption rate in
the case where the flow rate of the tertiary air 10 is adjusted
such that the O.sub.2 concentration in the exhaust gas of the
calciner 2 is 1.5% to 5%. Moreover, the O.sub.2 concentration in
the exhaust gas from the preheater 1 is affected not only by the
O.sub.2 concentration in the exhaust gas sent from the calciner 2
but also by the O.sub.2 concentration in the exhaust gas from the
cement kiln 3. FIG. 6 illustrates variation of the O.sub.2
concentration in the exhaust gas at the outlet of the preheater 1
and the heat consumption rate.
[0065] Notably, in this simulation, relation between the
aforementioned O.sub.2 concentration and the heat consumption rate
was analyzed with respect to each of three kinds of fuel ratios.
Herein, the fuel ratio=(heat amount of the fuel inputted to the
calciner 2)/(heat amount of the fuel inputted to the cement kiln
3+heat amount of the fuel inputted to the calciner 2).
[0066] From FIG. 5 and FIG. 6, in any case of these fuel ratios, it
appears that when the flow rate of the combustion air (tertiary air
10) in the calciner 2 is increased, the heat consumption rate does
not become monotonously worse but takes the optimum point. This is
because the increase of the combustion air (tertiary air 10) to the
calciner 2 in order to make the combustion at the calciner 2 better
decreases the take-away sensible heat along with the exhaust 16
from the cooler 4, and in addition to this, causes increase of the
take-away sensible heat due to the increase of the exhaust gas
temperature and the increase of the flow rate from the preheater
1.
[0067] Accordingly, the relations presented in FIG. 5 and FIG. 6
are beforehand obtained and, in operation, the first and second
oxygen concentrations are measured, and the fan and the flow rate
adjusting valve 11 which are provided in the exhaust line from the
cooler 4 are controlled such that both of these concentrations fall
within a range including the values of the oxygen concentrations at
which the aforementioned heat consumption rate becomes at its
minimum, to adjust the flow rate of the tertiary air fed to the
calciner and the flow rate of the exhaust 16 from the cooler 4. By
the adjustment described above, both the combustion at the calciner
2 and the heat consumption rate can be simultaneously optimized.
Notably, it is desirable that the O.sub.2 concentration in the
exhaust gas at the calciner outlet is adjusted to be approximately
2% to 4%, and the O.sub.2 concentration in the preheater exhaust
gas is adjusted to be approximately 0.5% to 2%.
INDUSTRIAL APPLICABILITY
[0068] According to the present invention, there can be provided a
method for operating a cement plant capable of simultaneously
optimizing both the combustion at the calciner and the heat
consumption rate.
REFERENCE SIGNS LIST
[0069] 1 Preheater [0070] 2 Calciner [0071] 2a, 6a O.sub.2
concentration meter [0072] 3 Cement kiln [0073] 4 Cooler [0074] 8
Pulverized coal (first fuel) [0075] 10 Tertiary air [0076] 11 Flow
rate adjusting valve [0077] 13 Pulverized coal (second fuel) [0078]
15 Secondary air [0079] 16 Exhaust
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